As an interface for a data processing apparatus and an IC card, a structure that uses a single end signal and a structure that uses a low amplitude differential signal are available. The single end signal is a signal having for example a TTL level (for example, 3.3 V). The differential signal is a signal having a level of for example ±200 mV. When a single end signal is used, the number of lines required therefor is the half of that for a differential signal. Thus, the number of signal lines does not increase, a single end signal has been widely used. On the other hand, when a differential signal is used, since the signal level is low, the power consumption can be decreased. In addition, as an advantage of a differential signal, it is not affected by noise.
When a conventional IC card is provided with an interface that uses a single end signal, if an interface that uses a differential signal is added to the IC card, it is desired to perform transmissions of both the single end signal and the differential signal so as to maintain the compatibility of the conventional IC card and the data processing apparatus. Normally, since the level of a single end signal is largely different from the level of a differential signal, different signal lines are used for their interfaces.
However, in the limited space of the IC card or the like, the number of signal lines cannot be easily increased. To solve such a problem, a structure that transmits and receives a single end signal using one of the signal lines for the differential signal may be considered. When such a structure, which transmits and receives a single end signal using only one of the differential signal lines is used, stray capacitances of a single end signal transmitter or a single end signal receiver may cause the differential signal lines to be an unbalanced state. In addition, when a communication is made with a single end signal at high speed, a dumping resistor should be disposed in series with the signal lines so as to prevent the single end signal from overshooting or undershooting. In addition, a termination resistor should be disposed in parallel with the signal lines of a differential signal. Thus, when an interface that uses these two types of signals is structured, the number of parts adversely increases.
Therefore, an object of the present invention is to provide a data processing apparatus, an IC card, and an IC card system that allow differential signal lines to be in a balanced state and that prevent the number of parts from being adversely increased.